how to get rid of marblized effect on negs?

Its hard to say what the cause of this problem is without being able to see the negatives. A high wash temperature could cause reticulation which might be what you are describing, but it would have to be near boiling and even then I doubt this is the cause.

I would suggest trying to rewash a single strip of negatives and see if the marbling goes away. It could be some type of oil or chemical which has not been removed.